Flexible shaft stabilizer

ABSTRACT

A flexible shaft construction to transmit rotational energy between a motor and a centrifuge rotor having a thin, long flexible shaft surrounded by a resilient sleeve and a stiff tubular member. The shaft, sleeve and tubular member are arranged so that there is no relative rotational motion between them.

United States Patent 1191 Lehman Dec.- 18, 1973 [54] FLEXIBLE SHAFTSTABILIZER 2,698,526 1/1955 Beier 64/1 V 2,827,229 3/1958 Blum 233/23 R[75] Lehman [61165], M- 2,878,992 3/1959 Pickels et al. 233/11 [73]Assignee: International Equipment Company, 2" l l x v l1 erson NeedhamHelghts Mass 2,725,188 11/1955 Scott 233/23 R [22] Filed: Nov. 22, 1971Prima Examiner-Geor e H. Krizmanich 21 A 1. N .1 201,069 g l pp 0Attorney-Herbert W. Kenway et al.

[52] US. Cl. 233/23 A, 64/1 V, 233/1 C i [51] Int. Cl B04b 9/14 [57]ABSTRACT 53 Fidd f Search 23 R, 1 C 23 R, A flexible shaft constructionto transmit rotational en- 233/23 A, 64 V R .ergy between a motor and acentrifuge rotor having a thin, long flexible shaft surrounded by aresilient 5 References Cited sleeve and a stiff tubular member. Theshaft, sleeve UNITED STATES PATENTS and tubular member are arranged sothat there is no relative rotational motion between them. 2,889,6956/1959 Moeller 64/1 V 2,476,894 7/1949 Mulheim .(64/1 V 4 Claims, 2Drawing Figures I FLEXIBLE SHAFT STABILIZER FLEXIBLE SHAFT CONSTRUCTIONThis invention relates to a flexible shaft construction employed totransmit rotational energy between a motor and a centrifuge rotor.

BACKGROUND OF THE INVENTION In bringing the rotation of a centrifugerotor up to the desired rotational speed, the shaft connecting the rotorand the motor passes through a phase known as the critical speed whereingreatly increased vibrations are encountered. It is desired to minimizevibrations to minimize the load on the motor bearings and to minimi zedvibrations in a gradient formed while centrifuging a sample in'therotor. The speed at which this occurs is dependent primarily upon thegeometry of the shaft and its elastic characteristics. Relatively stiffor thick short shafts encounter much more severe vibrations than doflexible or relatively thin long shafts. Therefore, it is preferred toemploy flexible, relatively thin, long shafts to obtain good sampleseparation. It also has been proposedto employ dampening means to reducethe vibrations encountered at the critical speed. However, while thedampening means reduces the severity of vibrations over a wider range ofrotational speeds as compared to an undampened shaft the degree ofvibration encountered still is undesirably high. Thus, the use ofdampening means has proven unsatisfactory for reducing the overallvibrational effect on the samples in the centrifuge rotor.

In applications wherein the vibrational effect must be minimized, suchas in blood separation, it is necessary to employ a flexible shaft as acoupling between the motor and the 'centrifuge rotor. Unfortunately, aflexible shaft having a long thin configuration is damaged easily,particularly while loading the centrifuge rotor with samples.Accordingly, it has been proposed to encase the rotating shaft with aflexible material structured so that the flexible material contacts ballbearings which in turn contact a flexible race attached to a stationaryhousing such as shown in U.S. Pat. No. 2,827,229. While the couplingremains flexible in this construction, the construction has twoseriousdrawbacks. First, it is very expensive to produce because of thehigh precision with which'a large number of parts must be assembled andsecond, the bearings within which the shaft rotates tends to confine theshaft thereby reducing its flexibility and thereby increasing thevibration the shaft experiences while rotating at the critical speed.

SUMMARY OF THE INVENTION The present invention provides a flexiblerotatable shaft coupling between a motor and acentrifuge rotor. Theconstruction comprises a long, thin, shaft being FIG. 2 is a crosssectional view taken along line 22 of FIG. 1.

DESCRIPTION OF PREFERRED EMBODIMENTS comprises a relatively thinelongated shaft 13 which is surrounded by a sleeve 14 made from aresilient material such' as natural or synthetic rubber. The sleeve 14is enclosed by a tubular member 15 made from a nonresilient structurallystrong material preferably a metal. The sleeve 14 and-shaft 13 are heldtogether by the frictional force between the adjacent surfaces thereofwhich prevents relative motion between shaft 13 and sleeve 14 duringrotation. The tubular member I5 is attached to the lower end 16 of shaft13 by screws-l7 and to the drive shaft 18 by screws 17 which clamps thetubular member 15 around end 16 and drive shaft 18. The centrifuge rotor10 is of conventional construction and comprises a metal body 20 andcompartments 21 into which are placed samples which are to be separated.In use, the centrifuge rotor 10 is placed upon drive shaft coupling 24and is retained thereon by con ventional means. Shaft 13 is attached tothe shaft coupling 24 such as by press fitting the upper end 16a into abore of the shaft coupling 24. Thus, during loading any deformation thatis effected to the shaft 13 is limited by means of bearing surfaces 14aon sleeve 14 which sleeve 14 in turn is restricted by the rigid tubularmember 15. With this construction, the chances of damaging shaft 13 aregreatly decreased particularly during this loading operation. Generally,the deformation on shaft 13 caused by unequal loading is in the order ofabout 5/1000 of an inch from the axial center I of shaft 13. Duringrotation, very little force is transmitconfined within a sleeve formedof a resilient material along a portion of its length and a cylindricalhollow tube which surrounds the shaft and do not move relative to theshaft. The shaft is provided with coupling.

means for the motor and the rotor.

BRIEF DESCRIPTION OF THE DRAWINGS ted to the motor after the criticalspeed has been reached because the shaft 13 becomes permanentlydeflected and thecenter of gravity of the centrifuge rotor 10 is thenover the axial'center of the shaft 13. The

mass added to the shaft 13 by the tubularmember I5 and the sleeve Mcause little or no increase in vibrations when the shaft 13 passesthrough the critical speed. Thus, there is no transmission of additionalvibration to the motor 11' and the bearings associated therewith ascompared with the shaft I3 alone. Accordingly, the present constructionprovides substantial advantages in view of the simplicity ofconstruction, the minimization of the vibrational effect on the shaft 13caused by the additional mass of the tubular member and the sleeve andthe safety from permanent damage tothe shaft caused by deformationthereof particularly during loading the rotor 10.

The shaft 13 should beflexible and have a length to diameter ratio suchthat there is sufficient flexibility to permit self-balancing to occurwithout effecting yield stresses on the shaft. Preferably the shaftlength to diameter ratio is between about 15 to one and 30 to one. Theshaft should be sufficiently flexible to permit its deformation withoutbeing permanently deformed. The sleeve 14 and tubular member 15preferably have equal lengths and extend to enclose nearly all thelength of the flexible shaft 13. The sleeve prevents restraint of theshaft by a force transferred directly'from the tubular member 15 andbecause the tubular member is relatively inelastic, it effectivelyprevents transmission of large forces to the shaft. It is understoodthat the sleeve 14 is not required in the present invention since thepermanent deflection of the shaft 13 during rotation is not sufficientto effect contact thereof with the tubular member 15. Alternatively, theinterior of the tubular member at the top portion thereof can beprovided with an elastic material such as rubber.

I claim:

1. A flexible shaft construction for transmitting rotational energybetween a centrifuge rotor and a motor which comprises a shaft having aregular horizontal cross section about its vertical axis, said shaftbeing sufficiently flexible when attached to a centrifuge rotor topermit self-balancing of the shaft to occur during rotation, said shafthaving means on a first end for being coupled to a motor and havingmeans on a second end for being coupled to a centrifuge rotor, a tubularmember attached to the first end of said shaft so that the shaft andtubular member do not rotate relative to each other during rotation, aresilient sleeve between said tubular member and shaft to preventcontact of said shaft and tubular member during rotation, said tubularmember having means at a first end for being coupled to a motor and tosaid first end of said shaft, said tubular member at a second end beingunattached and surrounding said shaft, said second end of said tubularmember positioned so that said shaft is located along the vertical axisof the tubular member and said tubular member and resilient sleevepositioned to prevent said shaft to be permanently deformed whilepermitting said shaft to be deflected by virtue of self balancing.

2. The construction of claim 1 wherein the length to diameter ratio ofthe shaft is between about 15 to one and 30 to one.

3. A centrifuge comprising a centrifuge rotor, a motor, a housing forsaid motor and a flexible shaft construction for transmitting rotationalenergy between the centrifuge rotor and the motor which comprises ashaft having a regular horizontal cross section about its vertical axis,said shaft being sufficiently flexible when attached to the cenrifugerotor to permit self balancing of the shaft to occur during rotation,said shaft having means on a first end for being coupled to the motorand having means on a second end for being coupled to the centrifugerotor, a tubular member attached to the first end of said shaft so thatthe shaft and tubular member do not rotate relative to each other duringrotation, a resilient sleeve between said tubular member and shaft toprevent contact of said shaft and tubular member during rotation, saidtubular member having means at a first end for being coupled to themotor and to said first end of said shaft, said tubular member at asecond end being unattached and surrounding said shaft, said second endof said tubular member positioned so that said shaft is located alongthe vertical axis of the tubular member and said tubular member andresilient sleeve positioned to prevent said shaft to be permanentlydeformed while permitting said shaft to be deflected by virtue ofself-balancing.

4. The centrifuge of claim 3 wherein the length to diameter ratio of theshaft is between about 15 to one and 30 to one.

1. A flexible shaft construction for transmitting rotational energy between a centrifuge rotor and a motor which comprises a shaft having a regular horizontal cross section about its vertical axis, said shaft being sufficiently flexible when attached to a centrifuge rotor to permit self-balancing of the shaft to occur during rotation, said shaft having means on a first end for being coupled to a motor and having means on a second end for being coupled to a centrifuge rotor, a tubular member attached to the first end of said shaft so that the shaft and tubular member do not rotate relative to each other during rotation, a resilient sleeve between said tubular member and shaft to prevent contact of said shaft and tubular member during rotation, said tubular member having means at a first end for being coupled to a motor and to said first end of said shaft, said tubular member at a second end being unattached and surrounding said shaft, said second end of said tubular member positioned so that said shaft is located along the vertical axis of the tubular member and said tubular member and resilient sleeve positioned to prevent said shaft to be permanently deformed while permitting said shaft to be deflected by virtue of self balancing.
 2. The construction of claim 1 wherein the length to diameter ratio of the shaft is between about 15 to one and 30 to one.
 3. A centrifuge comprising a centrifuge rotor, a motor, a housing for said motor and a flexible shaft construction for transmitting rotational energy between the centrifuge rotor and the motor which comprises a shaft having a regular horizontal cross section about its vertical axis, said shaft being sufficiently flexible when attached to the cenrifuge rotor to permit self balancing of the shaft to occur during rotation, said shaft having means on a first end for being coupled to the motor and having means on a second end for being coupled to the centrifuge rotor, a tubular member attached to the first end of said shaft so that the shaft and tubular member do not rotate relative to each other during rotation, a resilient sleeve between said tubular member and shaft to prevent contact of said shaft and tubular member during rotation, said tubular member having means at a first end for being coupled to the motor and to said first end of said shaft, said tubular member at a second end being unattached and surrounding said shaft, said second end of said tubular member positioned so that said shaft is located along the vertical axis of the tubular member and said tubular member and resilient sleeve positioned to prevent said shaft to be permanently deformed while permitting said shaft to be deflected by virtue of self-balancing.
 4. The centrifuge of claim 3 wherein the length to diameter ratio of the shaft is between about 15 to one and 30 to one. 